Up to half of the 3.5 million babies born annually in the United States are exposed to diagnostic ultrasound in utero. No adverse effects, and many benefits, have accrued to ultrasound's proper use during pregnancy, but these are lingering concerns about its possible effects on subtle aspects of intrauterine brain ontogeny and subsequent behavioral and intellectual development. The goal of this research is to evaluate the possible biobehavioral effects of ultrasound on the developing central nervous system by exposure of rat embryos and fetuses to ultrasound and evaluating the offspring with tests recently developed here and elsewhere to detect behavioral teratogenicity. The structural and ponderal teratogenicity of ultrasound in separate groups identically exposed will also be evaluated. A unique feature of the proposal is that we will insonate rats without subjecting them to long periods of anesthesia or other forced restraint during gestation by using a behavioral approach in which we will train the rats to voluntarily remain stationary while propping themselves in a water vessel. We already have data that this can be done successfully. In the course of 5 years we propose to examine the dose-response effects of continuous wave (yr-01) and pulsed wave (yr-02) ultrasound (4 levels of each type, 2-3 of which are in the clinical range). Exposure will be during most of pregnancy (postimplantation to parturition). The structural, ponderal, neurological, and behavioral development of the offspring will be evaluated in detail. We will also determine if ultrasound produces any residual maternal effects lasting until after delivery that might affect the dam's rearing of her young (yr-03). Finally, we will assess whether ultrasound at one of four very specific stages of gestation has any effects on postnatal neurological, behavioral, and intellectual development (yr-04 & 05). The stages of exposure for this last 2-year study will be preimplantation, early-mid organogenesis, late organogenesis, and fetogenesis, all stages that are clinically relevant.